Optical system, optical apparatus, and method for manufacturing optical system

ABSTRACT

An optical system used in an optical apparatus, such as a camera  1 , is configured to include a plurality of lens groups such that at focusing the distances between the lens groups are varied, that a final lens group disposed closest to an image side of the lens groups includes at least one lens surface having a pole, and that all of the following conditional expressions are satisfied: 
       0.020&lt; Y/f &lt;0.120  (1)
 
       0.010&lt; Bf/TL &lt;0.150  (2)
 
     where Y is image height, f is the focal length of the optical system, TL is the total optical length of the optical system, and Bf is the back focus of the optical system.

FIELD

The present invention relates to an optical system, an optical apparatus, and a method for manufacturing an optical system.

BACKGROUND

Optical systems used in optical apparatuses, such as cameras for photographs, electronic still cameras, and video cameras, have been proposed (see, e.g., Patent Literature 1).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Publication No. 2018-072457

SUMMARY

An optical system of the present disclosure includes a plurality of lens groups, at focusing the distances between the lens groups are varied, a final lens group disposed closest to an image side of the lens groups includes at least one lens surface having a pole, and all of the following conditional expressions are satisfied:

0.020<Y/f<0.120

0.010<Bf/TL<0.150

where

Y is image height,

f is the focal length of the optical system,

TL is the total optical length of the optical system, and

Bf is the back focus of the optical system.

A method for manufacturing an optical system of the present disclosure is a method for manufacturing an optical system including a plurality of lens groups, at focusing the distances between the lens groups are varied, a final lens group disposed closest to an image side of the lens groups includes at least one lens surface having a pole, and the method includes arranging so that all of the following conditional expressions are satisfied:

0.020<Y/f<0.120

0.010<Bf/TL<0.150

where

Y is image height,

f is the focal length of the optical system,

TL is the total optical length of the optical system, and

Bf is the back focus of the optical system.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an optical system of a first example focusing on an object at infinity.

FIG. 2A shows aberrations of the optical system of the first example focusing on an object at infinity.

FIG. 2B shows aberrations of the optical system of the first example focusing on a nearby object.

FIG. 3 is a cross-sectional view of an optical system of a second example focusing on an object at infinity.

FIG. 4A shows aberrations of the optical system of the second example focusing on an object at infinity.

FIG. 4B shows aberrations of the optical system of the second example focusing on a nearby object.

FIG. 5 is a cross-sectional view of an optical system of a third example focusing on an object at infinity.

FIG. 6A shows aberrations of the optical system of the third example focusing on an object at infinity.

FIG. 6B shows aberrations of the optical system of the third example focusing on a nearby object.

FIG. 7 schematically shows a camera including an optical system of the embodiment.

FIG. 8 is a flowchart outlining a method for manufacturing an optical system of the embodiment.

DESCRIPTION OF EMBODIMENTS

The following describes an optical system, an optical apparatus, and a method for manufacturing an optical system of an embodiment of the present application.

An optical system of the present embodiment includes a plurality of lens groups, at focusing the distances between the lens groups are varied, a final lens group disposed closest to an image side of the lens groups includes at least one lens surface having a pole, and all of the following conditional expressions are satisfied. A pole in the present disclosure refers to a point on a lens surface, other than on an optical axis, at which the tangent plane of the lens surface crosses the optical axis perpendicularly.

0.020<Y/f<0.120  (1)

0.010<Bf/TL<0.150  (2)

where

Y is image height,

f is the focal length of the optical system,

TL is the total optical length of the optical system, and

Bf is the back focus of the optical system.

The optical system of the present embodiment, in which the final lens group includes a lens surface having a pole, can reduce axial and off-axis aberrations effectively.

The optical system of the present embodiment can correct off-axis aberrations of image height, such as coma aberration, favorably by setting the value of conditional expression (1) less than the upper limit. The effect of the optical system of the present embodiment can be further ensured by setting the upper limit of conditional expression (1) at 0.120. To further ensure the effect of the present embodiment, the upper limit of conditional expression (1) is preferably set at 0.110, 0.100, 0.095, 0.090, 0.085, 0.080, 0.075, 0.070, 0.065, 0.063, or 0.060, more preferably at 0.058.

The optical system of the present embodiment can correct chromatic aberration at an appropriate focal length favorably by setting the value of conditional expression (1) greater than the lower limit. The effect of the optical system of the present embodiment can be further ensured by setting the lower limit of conditional expression (1) at 0.020. To further ensure the effect of the present embodiment, the upper limit of conditional expression (1) is preferably set at 0.025, 0.028, 0.030, or 0.033, more preferably at 0.035.

In the present embodiment, setting the value of conditional expression (2) less than the upper limit prevents the back focus from being too long and the optical system from upsizing. The effect of the optical system of the present embodiment can be further ensured by setting the upper limit of conditional expression (2) at 0.150. To further ensure the effect of the present embodiment, the upper limit of conditional expression (2) is preferably set at 0.120, 0.100, 0.090, 0.085, or 0.080, more preferably at 0.075.

The optical system of the present embodiment can correct off-axis aberrations, such as coma aberration, favorably by setting the value of conditional expression (2) greater than the lower limit. The effect of the optical system of the present embodiment can be further ensured by setting the lower limit of conditional expression (2) at 0.010. To further ensure the effect of the present embodiment, the lower limit of conditional expression (2) is preferably set at 0.013, 0.015, 0.018, or 0.020, more preferably at 0.022.

A small-sized optical system of favorable imaging performance can be achieved by the above configuration.

In the optical system of the present embodiment, the at least one lens surface having a pole preferably satisfies the following conditional expression:

0.02<h/Y<1.20  (3)

where

h is the height from an optical axis of the pole closest to the optical axis on the lens surface having a pole.

The optical system of the present embodiment can correct axial aberration and off-axis aberrations, such as coma aberration, distortion, and curvature of field, in a balanced manner by satisfying conditional expression (3).

The effect of the optical system of the present embodiment can be further ensured by setting the upper limit of conditional expression (3) at 1.20. To further ensure the effect of the present embodiment, the upper limit of conditional expression (3) is preferably set at 1.15, 1.10, 1.05, or 1.00, more preferably at 0.95.

The effect of the optical system of the present embodiment can be further ensured by setting the lower limit of conditional expression (3) at 0.02. To further ensure the effect of the present embodiment, the lower limit of conditional expression (3) is preferably set at 0.05, 0.10, 0.25, 0.30, 0.35, 0.40, or 0.45, more preferably at 0.50.

The optical system of the present embodiment preferably includes one or more positive lenses that are lenses including the lens surface having a pole and that have positive refractive power, and at least one of the one or more positive lenses preferably satisfies the following conditional expression:

−0.15<(Dh−Dc)/rK<0.00  (4)-1

where

Dh is the thickness on an optical axis of a lens including the lens surface having a pole,

Dc is the thickness at the pole of the lens including the lens surface having a pole, and

rK is the effective radius of the lens including the lens surface having a pole.

The optical system of the present embodiment can correct curvature of field favorably and control the position of an exit pupil appropriately by satisfying conditional expression (4)-1.

The effect of the optical system of the present embodiment can be further ensured by setting the upper limit of conditional expression (4)-1 at 0.00. To further ensure the effect of the present embodiment, the upper limit of conditional expression (4)-1 is preferably set at −0.03, −0.05, or −0.08, more preferably at −0.10.

The effect of the optical system of the present embodiment can be further ensured by setting the lower limit of conditional expression (4)-1 at −0.15. To further ensure the effect of the present embodiment, the lower limit of conditional expression (4)-1 is preferably set at −0.13.

The optical system of the present embodiment preferably includes one or more negative lenses that are lenses including the lens surface having a pole and that have negative refractive power, and at least one of the one or more negative lenses preferably satisfies the following conditional expression:

0.000<(Dh−Dc)/rK<0.100  (4)-2

where

Dh is the thickness on an optical axis of a lens including the lens surface having a pole,

Dc is the thickness at the pole of the lens including the lens surface having a pole, and

rK is the effective radius of the lens including the lens surface having a pole.

The optical system of the present embodiment can correct curvature of field favorably and control the position of an exit pupil appropriately by satisfying conditional expression (4)-2.

The effect of the optical system of the present embodiment can be further ensured by setting the upper limit of conditional expression (4)-2 at 0.100. To further ensure the effect of the present embodiment, the upper limit of conditional expression (4)-2 is preferably set at 0.095, 0.090, 0.085, or 0.080, more preferably at 0.075.

The effect of the optical system of the present embodiment can be further ensured by setting the lower limit of conditional expression (4)-2 at 0.000. To further ensure the effect of the present embodiment, the lower limit of conditional expression (4)-2 is preferably set at 0.003, more preferably at 0.005.

The optical system of the present embodiment preferably satisfies the following conditional expression:

0.020<KML/TL<0.140  (5)

where

KML is the distance from the lens surface having a pole closest to an image plane to the image plane.

The optical system of the present embodiment can correct curvature of field favorably by setting the value of conditional expression (5) less than the upper limit. The effect of the optical system of the present embodiment can be further ensured by setting the upper limit of conditional expression (5) at 0.140. To further ensure the effect of the present embodiment, the upper limit of conditional expression (5) is preferably set at 0.135, 0.130, 0.125, or 0.120, more preferably at 0.118.

The optical system of the present embodiment can prevent reduction in the amount of ambient light by setting the value of conditional expression (5) greater than the lower limit. The effect of the optical system of the present embodiment can be further ensured by setting the lower limit of conditional expression (5) at 0.020. To further ensure the effect of the present embodiment, the lower limit of conditional expression (5) is preferably set at 0.025, 0.030, 0.035, 0.040, 0.045, or 0.050, more preferably at 0.055.

In the optical system of the present embodiment, at least one lens including the lens surface having a pole preferably satisfies the following conditional expression:

0.70<rK/Y<1.10  (6)

where

rK is the effective radius of the lens including the lens surface having a pole.

The optical system of the present embodiment can correct off-axis aberrations, such as coma aberration, distortion, and curvature of field, favorably by satisfying conditional expression (6).

The effect of the optical system of the present embodiment can be further ensured by setting the upper limit of conditional expression (6) at 1.10. To further ensure the effect of the present embodiment, the upper limit of conditional expression (6) is preferably set at 1.05, 1.00, or 0.98, more preferably at 0.95.

The effect of the optical system of the present embodiment can be further ensured by setting the lower limit of conditional expression (6) at 0.70. To further ensure the effect of the present embodiment, the lower limit of conditional expression (6) is preferably set at 0.73, 0.75, 0.78, or 0.80, more preferably at 0.82.

In the optical system of the present embodiment, at least one lens including the lens surface having a pole preferably satisfies the following conditional expression:

−0.40<Bf/fK<0.40  (7)

where

fK is the focal length of the lens including the lens surface having a pole.

The optical system of the present embodiment can control the position of an exit pupil appropriately and correct curvature of field favorably by satisfying conditional expression (7).

The effect of the optical system of the present embodiment can be further ensured by setting the upper limit of conditional expression (7) at 0.40. To further ensure the effect of the present embodiment, the upper limit of conditional expression (7) is preferably set at 0.38, 0.35, or 0.33, more preferably at 0.30.

The effect of the optical system of the present embodiment can be further ensured by setting the lower limit of conditional expression (7) at −0.40. To further ensure the effect of the present embodiment, the lower limit of conditional expression (7) is preferably set at −0.35, −0.30, −0.25, −0.20, or −0.15, more preferably at −0.10.

In the optical system of the present embodiment, at least one lens including the lens surface having a pole preferably satisfies the following conditional expression:

25.00<νdK<70.00  (8)

where

νdK is the Abbe number for d-line of the lens including the lens surface having a pole.

The optical system of the present embodiment can correct chromatic aberration favorably by satisfying conditional expression (8).

The effect of the optical system of the present embodiment can be further ensured by setting the upper limit of conditional expression (8) at 70.00. To further ensure the effect of the present embodiment, the upper limit of conditional expression (8) is preferably set at 68.00 or 66.00, more preferably at 65.00.

The effect of the optical system of the present embodiment can be further ensured by setting the lower limit of conditional expression (8) at 25.00. To further ensure the effect of the present embodiment, the lower limit of conditional expression (8) is preferably set at 30.00, 35.00, 38.00, or 40.00, more preferably at 42.00.

In the optical system of the present embodiment, at least one lens including the lens surface having a pole preferably satisfies the following conditional expression:

−1.00<fR/fK<0.60  (9)

where

fR is the focal length of the final lens group, and

fK is the focal length of the lens including the lens surface having a pole.

The optical system of the present embodiment can control the position of an exit pupil appropriately and correct curvature of field favorably by satisfying conditional expression (9).

The effect of the optical system of the present embodiment can be further ensured by setting the upper limit of conditional expression (9) at 0.60. To further ensure the effect of the present embodiment, the upper limit of conditional expression (9) is preferably set at 0.55, 0.50, 0.45, or 0.40, more preferably at 0.35.

The effect of the optical system of the present embodiment can be further ensured by setting the lower limit of conditional expression (9) at −1.00. To further ensure the effect of the present embodiment, the lower limit of conditional expression (9) is preferably set at −0.98, −0.95, or −0.93, more preferably at −0.90.

The optical system of the present embodiment preferably satisfies the following conditional expression:

−0.50<Bf/rR<0.20  (10)

where

rR is the radius of curvature of a lens surface disposed closest to the image side.

The optical system of the present embodiment can control the position of an exit pupil appropriately and correct curvature of field favorably by satisfying conditional expression (10).

The effect of the optical system of the present embodiment can be further ensured by setting the upper limit of conditional expression (10) at 0.20. To further ensure the effect of the present embodiment, the upper limit of conditional expression (10) is preferably set at 0.15, 0.10, or 0.05, more preferably at 0.02.

The effect of the optical system of the present embodiment can be further ensured by setting the lower limit of conditional expression (10) at −0.50. To further ensure the effect of the present embodiment, the lower limit of conditional expression (10) is preferably set at −0.48, −0.45, −0.43, −0.40, or −0.38, more preferably at −0.35.

In the optical system of the present embodiment, at least one lens including the lens surface having a pole preferably satisfies the following conditional expression:

−2.00<fK/f<0.50  (11)

where

fK is the focal length of the lens including the lens surface having a pole.

The optical system of the present embodiment can correct axial aberration and off-axis aberrations, such as coma aberration, distortion, and curvature of field, in a balanced manner by satisfying conditional expression (11).

The effect of the optical system of the present embodiment can be further ensured by setting the upper limit of conditional expression (11) at 0.50. To further ensure the effect of the present embodiment, the upper limit of conditional expression (11) is preferably set at 0.45, 0.40, 0.35, or 0.30, more preferably at 0.28.

The effect of the optical system of the present embodiment can be further ensured by setting the lower limit of conditional expression (11) at −2.00. To further ensure the effect of the present embodiment, the lower limit of conditional expression (11) is preferably set at −1.95, −1.90, −1.85, or −1.80, more preferably at −1.75.

The optical system of the present embodiment preferably satisfies the following conditional expression.

0.20<TL/f<1.10  (12)

The optical system of the present embodiment can be prevented from upsizing by setting the value of conditional expression (12) less than the upper limit. The effect of the optical system of the present embodiment can be further ensured by setting the upper limit of conditional expression (12) at 1.10. To further ensure the effect of the present embodiment, the upper limit of conditional expression (12) is preferably set at 1.08, 1.05, or 1.03, more preferably at 1.00.

The optical system of the present embodiment can correct aberrations favorably by setting the value of conditional expression (12) greater than the lower limit. The effect of the optical system of the present embodiment can be further ensured by setting the lower limit of conditional expression (12) at 0.20. To further ensure the effect of the present embodiment, the lower limit of conditional expression (12) is preferably set at 0.25, 0.30, 0.35, 0.40, or 0.43, more preferably at 0.45.

The optical system of the present embodiment preferably satisfies the following conditional expression.

0.005<Bf/f<0.100  (13)

In the present embodiment, setting the value of conditional expression (13) less than the upper limit prevents the back focus from being too long and the optical system from upsizing. The effect of the optical system of the present embodiment can be further ensured by setting the upper limit of conditional expression (13) at 0.100. To further ensure the effect of the present embodiment, the upper limit of conditional expression (13) is preferably set at 0.095, 0.090, 0.085, or 0.080, more preferably at 0.075.

The optical system of the present embodiment can prevent an exit pupil from being too near the image plane and correct off-axis aberrations, such as coma aberration, favorably by setting the value of conditional expression (13) greater than the lower limit. The effect of the optical system of the present embodiment can be further ensured by setting the lower limit of conditional expression (13) at 0.005. To further ensure the effect of the present embodiment, the lower limit of conditional expression (13) is preferably set at 0.008, 0.010, or 0.013, more preferably at 0.015.

The optical system of the present embodiment preferably includes at least one lens Z satisfying all of the following conditional expressions:

ndLZ+(0.01425×νdLZ)<2.12  (14)

νdLZ<35.00  (15)

0.702<θgFLZ+(0.00316×νdLZ)  (16)

where

ndLZ is the refractive index for d-line of the lens Z,

νdLZ is the Abbe number for d-line of the lens Z, and

θgFLZ is a partial dispersion ratio of the lens Z and is defined by the following equation:

θgFLZ=(ngLZ−nFLZ)/(nFLZ−nCLZ)

where the refractive indices for g-line, F-line, and C-line of the lens Z are denoted by ngLZ, nFLZ, and nCLZ, respectively.

The optical system of the present embodiment having such a configuration can correct aberrations favorably.

Setting the value of conditional expression (14) less than the upper limit prevents the Petzval sum from being too small and enables the optical system of the present embodiment to correct curvature of field favorably. The effect of the present embodiment can be further ensured by setting the upper limit of conditional expression (14) at 2.12. To further ensure the effect of the present embodiment, the upper limit of conditional expression (14) is preferably set at 2.10, more preferably at 2.08.

The optical system of the present embodiment can correct quadratic variance of axial chromatic aberration favorably by setting the value of conditional expression (15) less than the upper limit. The effect of the present embodiment can be further ensured by setting the upper limit of conditional expression (15) at 35.00. To further ensure the effect of the present embodiment, the upper limit of conditional expression (15) is preferably set at 33.50, 32.50, 31.00, or 30.00, more preferably at 28.50.

The optical system of the present embodiment can correct quadratic variance of axial chromatic aberration favorably by setting the value of conditional expression (16) greater than the lower limit. The effect of the present embodiment can be further ensured by setting the lower limit of conditional expression (16) at 0.702. To further ensure the effect of the present embodiment, the upper limit of conditional expression (17) is preferably set at 0.705, 0.708, 0.710, 0.712, or 0.714, more preferably at 0.716.

The optical system of the present embodiment preferably includes at least one lens X satisfying the following conditional expression:

80.00<νdLX  (18)

where

νdLX is the Abbe number for d-line of the lens X.

The optical system of the present embodiment including the lens X satisfying conditional expression (18) can correct chromatic aberration favorably.

The effect of the optical system of the present embodiment can be further ensured by setting the lower limit of conditional expression (18) at 80.00. To further ensure the effect of the present embodiment, the lower limit of conditional expression (18) is preferably set at 83.00, 85.00, 88.00, or 90.00, more preferably at 92.50.

In the optical system of the present embodiment, a lens group disposed closest to an object side preferably has positive refractive power.

A small-sized optical system of favorable imaging performance can be achieved by the above configuration.

An optical apparatus of the present embodiment includes the optical system having the above configuration. This enables achieving a small-sized optical apparatus of favorable imaging performance.

A method for manufacturing an optical system of the present embodiment is a method for manufacturing an optical system including a plurality of lens groups, at focusing the distances between the lens groups are varied, a final lens group disposed closest to an image side of the lens groups includes at least one lens surface having a pole, and the method includes arranging so that all of the following conditional expressions are satisfied:

0.020<Y/f<0.120  (1)

0.010<Bf/TL<0.150  (2)

where

Y is image height,

f is the focal length of the optical system,

TL is the total optical length of the optical system, and

Bf is the back focus of the optical system.

A small-sized optical system of favorable imaging performance can be manufactured by such a method for manufacturing an optical system.

Numerical Examples

Examples of the present application will be described below with reference to the drawings.

First Example

FIG. 1 is a cross-sectional view of an optical system of a first example focusing on an object at infinity.

The optical system of the present example includes a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power, in order from the object side.

The first lens group G1 includes a biconvex positive lens L1, a positive meniscus lens L2 convex on the object side, a biconvex positive lens L3, a biconcave negative lens L4, a biconvex positive lens L5, and a positive cemented lens composed of a biconcave negative lens L6 and a biconvex positive lens L7, in order from the object side.

The second lens group G2 includes a positive meniscus lens L8 convex on the object side.

The third lens group G3 includes a negative cemented lens composed of a biconvex positive lens L9 and a biconcave negative lens L10; an aperture stop S; a negative cemented lens composed of a positive meniscus lens L11 convex on the image side and a biconcave negative lens L12; a biconcave negative lens L13; a biconvex positive lens L14; a positive cemented lens composed of a biconvex positive lens L15 and a negative meniscus lens L16 convex on the image side; a biconvex positive lens L17; and a biconcave negative lens L18, in order from the object side.

An imaging device (not shown) constructed from CCD, CMOS or the like is disposed on an image plane I.

A filter FL1 is disposed between the optical system of the present example and the image plane I.

The optical system of the present example focuses by moving the second lens group G2 along the optical axis. When the focus is shifted from infinity to a nearby object, the second lens group G2 moves from the image side toward the object side.

In the optical system of the present example, the negative cemented lens composed of the positive meniscus lens L11 and the negative lens L12 and the negative lens L13, which are lenses included in the third lens group G3, are configured as a vibration reduction lens group movable so that movement has a component in a direction perpendicular to the optical axis to correct an image blur.

In the optical system of the present example, the object-side lens surface of the positive meniscus lens L17 and the image-side lens surface of the negative meniscus lens L18 included in the third lens group G3 have a pole. The positive meniscus lens L17 corresponds to a positive lens that is a lens including a lens surface having a pole and that has positive refractive power. In the optical system of the present example, the positive lens L5 corresponds to the lens Z, and the positive meniscus lens L2 and the positive lens L3 each correspond to the lens X.

Table 1 below shows specifications of the optical system of the present example. In Table 1, f, Fno, and TL denote the focal length, the f-number, and the total optical length of the optical system focusing on infinity, respectively, and Bf denotes the back focus of the optical system.

In [Lens specifications], m denotes the positions of optical surfaces counted from the object side, r the radii of curvature, d the surface-to-surface distances, nd the refractive indices for d-line (wavelength 587.6 nm), and νd the Abbe numbers for d-line. In [Lens specifications], the radius of curvature r=∞ means a plane. In [Lens specifications], the optical surfaces with “*” are aspherical surfaces.

In [Aspherical surface data], ASP denotes the optical surface corresponding to the aspherical surface data, K the conic constant, and A4 to A20 the spherical constants.

The aspherical surfaces are expressed by expression (a) below, where the height in a direction perpendicular to the optical axis is denoted by y, the distance along the optical axis from the tangent plane at the vertex of an aspherical surface to the aspherical surface at height y (a sag) by S (y), the radius of curvature of a reference sphere (paraxial radius of curvature) by r, the conic constant by K, and the nth-order aspherical coefficient by An. In the examples, the second-order aspherical coefficient A2 is 0. “E-n” denotes “×10^(−n).”

S(y)=(y ² /r)/{1+(1−K×y ² /r ²)^(1/2) }+A4×y4+A6×y6+A8×y ⁸ +A10×y ¹⁰ +A12×y ¹² +A14×y ¹⁴ +A16×y ¹⁶ +A18×y ¹⁸ +A20×y ²⁰  (a)

The unit of the focal lengths f, the radii of curvature r, and the other lengths listed in Table 1 is “mm.” However, the unit is not limited thereto because the optical performance of a proportionally enlarged or reduced optical system is the same as that of the original optical system.

The above reference symbols in Table 1 will also be used similarly in the tables of the other examples described below.

TABLE 1 [General specifications] f 390.00 Fno 2.90 Bf 28.455 image height 21.700 TL 387.455 2ω 6.34 [Lens specifications] m r d nd νd θgF  1) 480.771 9.450 1.518600 69.89  2) −1180.201 18.368  3) 190.470 12.100 1.433837 95.16  4) 1088.433 88.972  5) 121.568 12.850 1.433837 95.16  6) −317.679 1.750  7) −279.152 2.600 1.737999 32.26  8) 211.486 38.050  9) 226.884 7.300 1.663820 27.35 0.632 10) −226.482 0.300 11) −382.831 1.900 1.749504 35.33 12) 64.198 8.350 1.437001 95.10 13) −3151.863 D13 14) 79.158 5.700 1.627496 59.24 15) 889.670 D15 16) 87.296 4.800 1.698950 30.13 17) −247.699 1.200 1.881003 40.14 18) 52.070 7.100 19> ∞ 7.032 (aperture stop) 20) −370.162 2.900 1.846663 23.78 21) −85.379 1.200 1.496997 81.61 22) 78.949 3.884 23) −106.294 1.200 1.593190 67.90 24) 126.247 7.883 25) 84.389 3.000 1.720467 34.71 26) −937.027 35.448 27) 126.616 7.600 1.595510 39.21 28) −67.347 1.200 1.945944 17.98 29) −126.151 22.187 *30)  111.791 6.100 1.612660 44.46 *31)  −126.654 9.374 *32)  −69.987 1.200 2.001003 29.13 *33)  240.688 6.450 34) ∞ 2.000 1.516800 63.88 35) ∞ 20.005 [Aspherical surface data] ASP: 30th surface K: −0.0945 A4: 0.00E+00 A6: −3.70E−06 A8: 6.64E−10 A10: −4.66E−11 A12: 3.48E−14 A14: −1.08E−16 A16: −2.85E−20 A18: 4.77E−23 A20: 3.35E−26 ASP: 31st surface K: 2.8122 A4: 0.00E+00 A6: −4.69E−06 A8: −1.35E−09 A10: −3.95E−11 A12: −1.64E−14 A14: 8.73E−17 A16: −6.66E−20 A18: −6.27E−23 A20: −2.46E−26 ASP: 32nd surface K: 3.0000 A4: 0.00E+00 A6: −7.94E−06 A8: 9.42E−09 A10: 1.32E−11 A12: 2.48E−15 A14: 9.89E−17 A16: 4.73E−29 A18: 6.43E−32 A20: −3.53E−25 ASP: 33rd surface K: −1.0000 A4: 0.00E+00 A6: −8.82E−06 A8: 1.08E−08 A10: 5.92E−12 A12: 4.61E−14 A14: −6.54E−17 A16: −3.08E−29 A18: −7.29E−32 A20: 3.36E−25 [Focal length data of groups] Groups Starting surfaces Focal lengths G1 1 379.315 G2 14 138.094 G3 16 −85.999 [Variable distance data] At focusing on infinity At focusing on a nearby object D13 24.000 4.100 D15 4.000 23.900

FIG. 2A shows aberrations of the optical system of the first example focusing on an object at infinity. FIG. 2B shows aberrations of the optical system of the first example focusing on a nearby object.

In the graphs of aberrations, FNO and Y denote f-number and image height, respectively. More specifically, the graph of spherical aberration shows the f-number corresponding to the maximum aperture, the graphs of astigmatism and distortion show the maximum of image height, and the graph of coma aberration shows the values of image height. d and g denote d-line and g-line (wavelength 435.8 nm), respectively. In the graph of astigmatism, the solid lines and the broken lines show a sagittal plane and a meridional plane, respectively. The reference symbols in the graphs of aberrations of the present example will also be used in those of the other examples described below.

The graphs of aberrations suggest that the optical system of the present example effectively reduces variations in aberrations at focusing and has high optical performance.

Second Example

FIG. 3 is a cross-sectional view of an optical system of a second example focusing on an object at infinity.

The optical system of the present example includes a first lens group G1 having positive refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power, in order from the object side.

The first lens group G1 includes a positive meniscus lens L1 convex on the object side, a biconvex positive lens L2, a biconvex positive lens L3, a biconcave negative lens L4, a biconvex positive lens L5, and a negative cemented lens composed of a biconcave negative lens L6 and a positive meniscus lens L7 convex on the object side, in order from the object side.

The second lens group G2 includes a biconvex positive lens L8.

The third lens group G3 includes a positive meniscus lens L9 convex on the object side; an aperture stop S; a negative cemented lens composed of a biconvex positive lens L10 and a biconcave negative lens L11; a biconcave negative lens L12; a positive meniscus lens L13 convex on the object side; a negative cemented lens composed of a biconvex positive lens L14 and a biconcave negative lens L15; a biconvex positive lens L16; a biconcave negative lens L17; and a biconcave negative lens L18, in order from the object side.

An imaging device (not shown) constructed from CCD, CMOS or the like is disposed on an image plane I.

Filters FL1 and FL2 are disposed between the optical system of the present example and the image plane I.

The optical system of the present example focuses by moving the second lens group G2 along the optical axis. When the focus is shifted from infinity to a nearby object, the second lens group G2 moves from the image side toward the object side.

In the optical system of the present example, the object-side lens surface of the negative lens L18 included in the third lens group G3 has a pole. The negative lens L18 corresponds to a negative lens that is a lens including a lens surface having a pole and that has negative refractive power. In the optical system of the present example, the positive lens L5 corresponds to the lens Z, the positive lenses L2 and L3 each correspond to the lens X.

Table 2 below shows specifications of the optical system of the present example.

TABLE 2 [General specifications] f 588.00 Fno 4.09 Bf 24.200 image height 21.700 TL 458.000 2ω 4.14 [Lens specifications] m r d nd νd θgF  1) 318.082 10.293 1.518600 69.89  2) 2767.474 70.000  3) 250.000 11.741 1.433837 95.16  4) −2625.391 76.022  5) 117.178 13.094 1.433837 95.16  6) −358.058 0.243  7) −326.721 2.600 1.737999 32.26  8) 219.472 44.906  9) 136.873 7.129 1.663820 27.35 0.632 10) −279.195 0.100 11) −417.537 1.900 1.800999 34.97 12) 57.256 8.730 1.437001 95.10 13) 422.344 D13 14) 75.383 6.241 1.518230 58.82 15) −1118.853 D15 16) 121.757 1.200 1.497820 82.57 17) 42.268 8.586 18> ∞ 6.500 (aperture stop) 19) 153.272 5.178 1.808090 22.74 20) −85.972 1.200 1.772500 49.62 21) 74.810 3.582 22) −107.276 1.200 1.816000 46.59 23) 255.014 4.500 24) 45.618 4.111 1.698950 30.13 25) 130.848 35.282 26) 102.108 7.814 1.698950 30.13 27) −26.600 1.260 1.922860 20.88 28) 212.812 0.460 *29)  50.919 10.000 1.647690 33.72 *30)  −30.632 0.100 31) −43.062 1.200 1.593190 67.90 32) 52.042 50.049 *33)  −119.867 3.013 1.848500 43.79 *34)  221837.780 6.000 35) ∞ 2.000 1.516800 64.13 36) ∞ 14.500 37) ∞ 1.600 1.516800 64.13 38) ∞ 0.100 [Aspherical surface data] ASP: 29th surface K: −3.5347 A4: 0.00E+00 A6: 3.84E−06 A8: 6.41E−10 A10: −3.33E−12 A12: 1.1E−14 ASP: 30th surface K: 1.24E+00 A4: 0.00E+00 A6: 8.39E−06 A8: 4.06E−09 A10: −3.49E−12 A12: 1.88E−14 ASP: 33rd surface K: 2.32E+01 A4: 0.00E+00 A6: 6.44E−06 A8: 2.40E−08 A10: −6.37E−11 A12: 5.19E−14 ASP: 34th surface K: −2.27E+29 A4: 0.00E+00 A6: 2.46E−06 A8: 2.50E−08 A10: −5.95E−11 A12: 3.75E−14 [Focal length data of groups] Groups Starting surfaces Focal lengths G1 1 445.504 G2 14 136.523 G3 16 −44.174 [Variable distance data] At focusing on infinity At focusing on a nearby object D13 31.468 17.198 D15 4.100 18.370

FIG. 4A shows aberrations of the optical system of the second example focusing on an object at infinity. FIG. 4B shows aberrations of the optical system of the second example focusing on a nearby object.

The graphs of aberrations suggest that the optical system of the present example effectively reduces variations in aberrations at focusing and has high optical performance.

Third Example

FIG. 5 is a cross-sectional view of an optical system of a third example focusing on an object at infinity.

The optical system of the present example includes a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having negative refractive power, in order from the object side. An aperture stop S is disposed between the first lens group G1 and the second lens group G2.

The first lens group G1 includes a positive meniscus lens L1 convex on the object side; a positive meniscus lens L2 convex on the object side; a negative meniscus lens L3 convex on the object side and having a multilayered and glued diffractive optical element GD made of two different materials on the image-side lens surface; a negative cemented lens composed of a biconvex positive lens L4 and a biconcave negative lens L5; a positive meniscus lens L6 convex on the object side; and a positive cemented lens composed of a negative meniscus lens L7 convex on the object side and a positive meniscus lens L8 convex on the object side, in order from the object side.

The second lens group G2 includes a biconcave negative lens L9.

The third lens group G3 includes a positive cemented lens composed of a negative meniscus lens L10 convex on the object side and a biconvex positive lens L11; a negative cemented lens composed of a biconvex positive lens L12 and a biconcave negative lens L13; a biconcave negative lens L14; a positive cemented lens composed of a biconvex positive lens L15 and a biconcave negative lens L16; a negative cemented lens composed of a biconvex positive lens L17 and a biconcave negative lens L18; a positive cemented lens composed of a biconvex positive lens L19 and a negative meniscus lens L20 convex on the image side; and a negative meniscus lens L21 convex on the image side, in order from the object side.

An imaging device (not shown) constructed from CCD, CMOS or the like is disposed on an image plane I.

The optical system of the present example focuses by moving the second lens group G2 along the optical axis. When the focus is shifted from infinity to a nearby object, the second lens group G2 moves from the object side toward the image side.

In the optical system of the present example, the negative cemented lens composed of the positive lens L12 and the negative lens L13 and the negative lens L14, which are lenses included in the third lens group G3, are configured as a vibration reduction lens group movable so that movement has a component in a direction perpendicular to the optical axis to correct an image blur.

In the optical system of the present example, the object-side and image-side lens surfaces of the negative meniscus lens L21 included in the third lens group G3 has a pole. The negative meniscus lens L21 corresponds to a negative lens that is a lens including a lens surface having a pole and that has negative refractive power. In the optical system of the present example, the positive meniscus lens L8 corresponds to the lens Z.

Table 3 below shows specifications of the optical system of the present example.

[Diffracting optical surface data] shows n (order of diffracted light), λ0 (designed wavelength), and C2 and C4 (phase coefficients) in the following equation (b) representing the phase shape ψ of the diffracting optical surface.

ψ(h,n)=(2π/(n×λ0))×(C2h ² +C4h ⁴)  (b)

TABLE 3 [General specifications] f 581.97 Fno 8.06 Bf 16.167 image height 21.600 TL 269.235 2ω 4.17 [Lens specifications] m r d nd νd θgF  1) 134.048 7.530 1.518600 69.89  2) 975.941 0.600  3) 93.756 8.246 1.518600 69.89  4) 332.255 9.686  5) 136.607 4.312 1.516800 64.13  6) 120.104 0.300 1.528300 36.18  7) 119.767 0.200 1.548900 51.30  8) 120.755 41.847  9) 88.622 5.436 1.518600 69.89 10) −416.992 2.000 1.903660 31.27 11) 41.602 5.323 12) 42.525 5.649 1.518600 69.89 13) 143.662 14.506 14) 47.751 2.000 1.903660 31.27 15) 28.892 4.794 1.663820 27.35 0.632 16) 112.282 11.734 17> ∞ D17 (aperture stop) 18) −1154.419 1.200 1.487490 70.32 19) 62.576 D19 20) 310.300 1.200 2.000690 25.46 21) 26.935 3.449 1.603420 38.03 22) −47.327 1.500 23) 48.394 3.086 1.672700 32.18 24) −44.128 1.100 1.497820 82.57 25) 26.495 2.410 26) −53.275 1.100 1.696800 55.52 27) 43.809 1.500 28) 24.114 4.701 1.603420 38.03 29) −25.443 1.200 1.497820 82.57 30) 29.757 8.994 31) 27.240 5.426 1.603420 38.03 32) −31.131 1.200 1.772500 49.62 33) 19.933 0.100 34) 20.086 7.524 1.603420 38.03 35) −18.471 1.200 1.922860 20.88 36) −83.172 44.826 *37)  −82.638 4.000 1.516800 64.13 *38)  −100.000 16.167 [Aspherical surface data] ASP: 37th surface K: 1.0000 A4: 0.00E+00 A6: 2.01E−05 ASP: 38th surface K: −3.4854 A4: 0.00E+00 A6: 1.93E−05 A8: −8.37E−09 A10: 7.40E−11 A12: −1.81E−13 [Diffracting optical surface data] GD: 7th surface n λ0 C2 C4 1 587.6 −3.59E−05 −9.39E−10 [Focal length data of groups] Groups Starting surfaces Focal lengths G1 1 173.592 G2 18 −121.724 G3 20 −78.037 [Variable distance data] At focusing on infinity At focusing on a nearby object D17 2.053 20.426 D19 31.136 12.840

FIG. 6A shows aberrations of the optical system of the third example focusing on an object at infinity. FIG. 6B shows aberrations of the optical system of the third example focusing on a nearby object.

The graphs of aberrations suggest that the optical system of the present example effectively reduces variations in aberrations at focusing and has high optical performance.

A small-sized optical system of favorable imaging performance can be achieved according to the above examples.

The following is a list of the conditional expressions and the values for the conditional expressions in the examples.

Y is image height, f is the focal length of the optical system, TL is the total optical length of the optical system, and Bf is the back focus of the optical system. h is the height from an optical axis of the pole closest to the optical axis on the lens surface having a pole. Dh is the thickness on an optical axis of a lens including the lens surface having a pole, Dc is the thickness at the pole of the lens including the lens surface having a pole, and rK is the effective radius of the lens including the lens surface having a pole.

KML is the distance from the lens surface having a pole closest to an image plane to the image plane. fK is the focal length of the lens including the lens surface having a pole. νdK is the Abbe number for d-line of the lens including the lens surface having a pole. fR is the focal length of the final lens group. rR is the radius of curvature of a lens surface disposed closest to the image side.

ndLZ is the refractive index for d-line of the lens Z, and θgFLZ is a partial dispersion ratio of the lens Z and is defined by the following equation:

θgFLZ=(ngLZ−nFLZ)/(nFLZ−nCLZ)

where the refractive indices for g-line, F-line, and C-line of the lens Z are denoted by ngLZ, nFLZ, and nCLZ, respectively.

νdLX is the Abbe number for d-line of the lens X.

[List of Conditional Expressions and their Values]

Conditional expressions: First example Second example Third example (1) Y/f: 0.056 0.037 0.037 (2) Bf/TL: 0.073 0.053 0.060 (3) h/Y: 0.724 0.915 0.571 (4) (Dh-Dc)/rK: −0.105 0.073 0.009 (5) KML/TL: 0.073 0.053 0.060 (6) rK/Y: 0.943 0.924 0.838 (7) Bf/fK: 0.291 −0.171 −0.016 (8) vdK: 29.13 43.79 64.13 (9) fR/fK: −0.879 0.313 0.078 (10)  Bf/rR: 0.118 0.000 −0.162 (11)  fK/f: 0.251 −0.240 −1.717 (12)  TL/f: 0.993 0.779 0.463 (13)  Bf/f: 0.073 0.041 0.028 (14)  ndLZ + (0.01425*vdLZ): 2.054 2.054 2.054 (15)  vdLZ: 27.35 27.35 27.35 (16)  θgFLZ + (0.00316*vdLZ: 0.718 0.718 0.718 (17)  vdLX: 95.16 95.16

The above examples illustrate specific examples of the present invention, and the present invention is not limited thereto. The following details can be appropriately employed unless the optical performance of the optical system of the embodiment of the present application is lost.

The lens surfaces of the lenses constituting any of the optical systems of the above examples may be covered with antireflection coating having high transmittance in a wide wavelength range. This reduces flares and ghosts, and enables achieving optical performance with high contrast.

Next, a camera including the optical system of the present embodiment is described with reference to FIG. 23 .

FIG. 23 schematically shows a camera including the optical system of the present embodiment.

The camera 1 is a “mirror-less camera” of an interchangeable lens type including the optical system according to the first example as an imaging lens 2.

In the camera 1, light from an object (subject) (not shown) is condensed by the imaging lens 2 and reaches an imaging device 3. The imaging device 3 converts the light from the subject to image data. The image data is displayed on an electronic view finder 4. This enables a photographer who positions his/her eye at an eye point EP to observe the subject.

When a release button (not shown) is pressed by the photographer, the image data is stored in a memory (not shown). In this way, the photographer can take a picture of the subject with the camera 1.

The optical system of the first example included in the camera 1 as the imaging lens 2 is a small-sized optical system of favorable optical performance. Thus the camera 1 can be small and achieve favorable optical performance. A camera configured by including the optical system of the second or third example as the imaging lens 2 can have the same effect as the camera 1.

Finally, a method for manufacturing an optical system of the present embodiment is described in outline with reference to FIG. 8 .

FIG. 8 is a flowchart outlining a method for manufacturing an optical system of the present embodiment.

The method for manufacturing an optical system of the present embodiment shown in FIG. 8 is a method for manufacturing an optical system including a plurality of lens groups and includes the following steps S1 to S4:

Step S1: preparing a plurality of lens groups;

Step S2: arranging so that at focusing the distances between the lens groups are varied;

Step S3: arranging so that a final lens group disposed closest to an image side of the lens groups includes at least one lens surface having a pole; and

Step S3: making the optical system satisfy all of the following conditional expressions:

0.020<Y/f<0.120  (1)

0.010<Bf/TL<0.150  (2)

where

Y is image height,

f is the focal length of the optical system,

TL is the total optical length of the optical system, and

Bf is the back focus of the optical system.

A small-sized optical system of favorable imaging performance can be manufactured by the method for manufacturing an optical system of the present embodiment.

Note that those skilled in the art can make various changes, substitutions, and modifications without departing from the spirit and scope of the present invention.

REFERENCE SIGNS LIST

-   -   S aperture stop     -   I image plane     -   1 camera     -   2 imaging lens     -   3 imaging device 

1. An optical system comprising a plurality of lens groups, at focusing the distances between the lens groups being varied, a final lens group disposed closest to an image side of the lens groups including at least one lens surface having a pole, all of the following conditional expressions being satisfied: 0.020<Y/f<0.120 0.010<Bf/TL<0.150 where Y is image height, f is the focal length of the optical system, TL is the total optical length of the optical system, and Bf is the back focus of the optical system.
 2. The optical system according to claim 1, wherein the at least one lens surface having a pole satisfies the following conditional expression: 0.02<h/Y<1.20 where h is the height from an optical axis of the pole closest to the optical axis on the lens surface having a pole.
 3. The optical system according to claim 1, comprising one or more positive lenses that are lenses including the lens surface having a pole and that have positive refractive power, wherein at least one of the one or more positive lenses satisfies the following conditional expression: −0.15<(Dh−Dc)/rK<0.00 where Dh is the thickness on an optical axis of a lens including the lens surface having a pole, Dc is the thickness at the pole of the lens including the lens surface having a pole, and rK is the effective radius of the lens including the lens surface having a pole.
 4. The optical system according to claim 1, comprising one or more negative lenses that are lenses including the lens surface having a pole and that have negative refractive power, wherein at least one of the one or more negative lenses satisfies the following conditional expression: 0.000<(Dh−Dc)/rK<0.100 where Dh is the thickness on an optical axis of a lens including the lens surface having a pole, Dc is the thickness at the pole of the lens including the lens surface having a pole, and rK is the effective radius of the lens including the lens surface having a pole.
 5. The optical system according to claim 1, wherein the following conditional expression is satisfied: 0.020<KML/TL<0.140 where KML is the distance from the lens surface having a pole closest to an image plane to the image plane.
 6. The optical system according to claim 1, wherein at least one lens including the lens surface having a pole satisfies the following conditional expression: 0.70<rK/Y<1.10 where rK is the effective radius of the lens including the lens surface having a pole.
 7. The optical system according to claim 1, wherein at least one lens including the lens surface having a pole satisfies the following conditional expression: −0.40<Bf/fK<0.40 where fK is the focal length of the lens including the lens surface having a pole.
 8. The optical system according to claim 1, wherein at least one lens including the lens surface having a pole satisfies the following conditional expression: 25.00<νdK<70.00 where νdK is the Abbe number for d-line of the lens including the lens surface having a pole.
 9. The optical system according to claim 1, wherein at least one lens including the lens surface having a pole satisfies the following conditional expression: −1.00<fR/fK<0.60 where fR is the focal length of the final lens group, and fK is the focal length of the lens including the lens surface having a pole.
 10. The optical system according to claim 1, wherein the following conditional expression is satisfied: −0.50<Bf/rR<0.20 where rR is the radius of curvature of a lens surface disposed closest to the image side.
 11. The optical system according to claim 1, wherein at least one lens including the lens surface having a pole satisfies the following conditional expression: −2.00<fK/f<0.50 where fK is the focal length of the lens including the lens surface having a pole.
 12. The optical system according to claim 1, wherein the following conditional expression is satisfied: 0.20<TL/f<1.10.
 13. The optical system according to claim 1, wherein the following conditional expression is satisfied: 0.005<Bf/f<0.100.
 14. The optical system according to claim 1, comprising at least one lens Z satisfying all of the following conditional expressions: ndLZ+(0.01425×νdLZ)<2.12 νdLZ<35.00 0.702<θgFLZ+(0.00316×νdLZ) where ndLZ is the refractive index for d-line of the lens Z, νdLZ is the Abbe number for d-line of the lens Z, and θgFLZ is a partial dispersion ratio of the lens Z and is defined by the following equation: θgFLZ=(ngLZ−nFLZ)/(nFLZ−nCLZ) where the refractive indices for g-line, F-line, and C-line of the lens Z are denoted by ngLZ, nFLZ, and nCLZ, respectively.
 15. The optical system according to claim 1, comprising at least one lens X satisfying the following conditional expression: 80.00<νdLX where νdLX is the Abbe number for d-line of the lens X.
 16. The optical system according to claim 1, wherein a lens group disposed closest to an object side has positive refractive power.
 17. An optical apparatus comprising the optical system according to claim
 1. 18. A method for manufacturing an optical system including a plurality of lens groups, at focusing the distances between the lens groups being varied, a final lens group disposed closest to an image side of the lens groups including at least one lens surface having a pole, the method comprising arranging so that all of the following conditional expressions are satisfied: 0.020<Y/f<0.120 0.010<Bf/TL<0.150 where Y is image height, f is the focal length of the optical system, TL is the total optical length of the optical system, and Bf is the back focus of the optical system. 